88 
FLOWERS AND INSECTS 
(5) Lepidoptera (butterflies and moths) : most species flower- visiting. 
Their tongues are on the whole about as long as those of bees, but 
some species, mostly Sphingidae (hawk-moths), have them of extra- 
ordinary lengths, e.g. in Britain that of Sphinx convolvuli is 80 mm. 
long, whilst some forms even reach 300 mm. 
For further details see Muller’s Fertilisation of Flowers and entomo- 
logical text-books. 
Insects have to be attracted to the flower and paid in 
useful material— honey, pollen, &c. — if they are to be 
regular visitors of any real use. When insect-pollination 
began, the attraction of insects from a distance, and their 
remuneration on arrival, were probably both functions of 
the androeceum. Afterwards differentiation began, and 
other modes of attraction and remuneration appeared. 
Pollen is an important part of the food of many insects ; 
many flowers depend largely upon it as an attraction. 
There exists a class of flowers, Po in Muller’s classification, 
which only furnishes pollen to visitors, having no honey. 
Such flowers are Hypericum sp., Spiraea sp. {e.g. common 
meadow-sweet), Helianthemum, Cytisus sp., Clematis sp., 
Rosa canina , &c. It is highly improbable that any of these 
are primitive pollen-flowers ; they are probably mostly 
flowers which have gradually lost their honey-secreting 
functions. They belong, structurally, to various groups of 
the honey-flowers, e.g. AB and H. They are always, however, 
in ecological work, retained as a separate class ; their visitors 
are mostly flies and pollen-collecting bees. Interesting cases 
of division of labour among the stamens of a single flower, 
some providing pollen for insects, some for pollination, occur 
in Cassia, Heeria, Commelina, &c. 
The secretion of honey, by special organs termed nectaries , 
is almost universal in entomophilous flowers. The nectaries 
are usually at the base of the flower. They may be upon 
the receptacle as in Malva, Compositae, &c., calyx as in 
Coronilla, petals as in Ranunculus, Swertia, &c., stamens as 
in Cruciferae and Caryophyllaceae, or carpels as in Caltha, 
Allium, &c. Sometimes they are themselves modified 
flower-leaves as in Nigella, Aconitum, &c., or parts of them 
as in Viola. The honey is protected from rain in many 
ways ; we shall consider the chief of these in dealing with 
the gradual evolution of tubes in flowers. Hairs often serve 
